I get prescribed Metformin. The local pharmacies only carry the 1000 mg size tablet. So doc prescribes the only available pill size and I cut them in half.

Children sometimes get prescribed medication that a pharmacy might only stock in an adult dose pill. If the pills are small, a pill cutter is a lot safer than splitting them with a knife.

Another application would be if a doctor recommends reducing the dose, but you still have a lot of the originally prescribed pills.

People who have to regularly take half a pill sometimes struggle with breaking the pill into clean halves, or don't like having to use a kitchen knife or whatever and clean it later.

breaking pills in half when you're 80 years old, and breaking 20 pills a week by hand bruises your palm.